a testbed for multi-antenna applications in rfid

A Testbed for Multi-Antenna Applications in RFID

Robert Langwieser, Christoph Angerer, andArpad L. Scholtz

RadioTecC 2009, Berlin

Christian Doppler Laboratory for Wireless Technologies for Sustainable Mobility 2

Outline

• Overview

• Reader - tag communication in passive RFID systems

• Testbed concept • Digital baseband • Analog frontends

• Antenna configurations

• Measurement example

• Outlook

• Summary


RFID – Radio Frequency Identification

• Radio technology allows non line-of-sight identification• Many applications: supply chain, logistics, access control,

library systems, etc. • Operated in various frequency ranges:

3


Passive – Semi-active - Active Tags

• Passive tags:• No internal power supply• Powered by the electromagnetic field of the reader• Communication: backscatter / load modulation

• Semi-active (semi-passive) tags: • Internal power supply• Communication: backscatter / load modulation

• Active tags: • Internal power supply• Active communication


Reader – Tag Communication

• Tag is powered by the reader • Crosstalk from transmitter to receiver at the reader• Tag response gets interfered by the crosstalk• Energy transfer from reader to tag during the whole communication• Crosstalk depends on the reader-antenna configuration


Requirements for the Testbed

• Multi-standard and multi-frequency• Real time operation• Flexibility due to modular implementation and reconfigurable

components• Available for many different scenarios• Mobility• Exploration of system parameters• Configuration of system parameters• Automated measurements • Reasonable setup time


Testbed Concept

DSP:TI TMS320C6416600MHz Fixed pointProtocol processing

ADCs and DACs (2x):14 / 16 bit40 MHz

7

FPGA:Xilinx Virtex II40 MHz Signal processing

RF frontends:HF and UHFCarrier suppressionEnvelope demodulator

Antennas:Commercially availablePrototypesMono-static, Bi-static


Rapid Prototyping Board

power supply

ethernet connection

DACs out / ADCs in

available: Austrian Institute of Technology – www.smart-systems.at


UHF Frontend Concept


UHF Receiver

CCIN

868 MHz

RXIN

868 MHz

LO2IN1006 MHz0 dBm

LO1IN

153.33 MHz-5 dBm

RXOUT

13.33 MHz

EDOUT power supply,control lines

• FR4 substrate• Multi layer printed circuit board (4 layers)• Off-the-shelf components


UHF Frontend System Parameters

• Frequency: 865MHz - 868MHz• 13.33 MHz interface frequency with the DSP/FPGA-hardware• Communication range: up to 10m• 2 W linear output power• Gain adjustment range at transmitters: 56 dB• Maximum receiver gain: 43 dB• Gain adjustment range at receiver: 55 dB• Maximum receiver input power: -8dBm • Mono-static and bi-static antenna configurations possible• Any 2×2 antenna configuration• Carrier to sideband ratio improvement (carrier suppression)• Gain settings manually via jumpers or remotely via microcontroller


Mono-static – Bi-static Antenna Configurations

Mono-static Bi-static

Crosstalk influenced by:• Antenna matching • Proximity effects • Reflections at objects• Antenna polarization• Circulator or directional coupler

Crosstalk influenced by:• Radiation pattern • Spatial configuration• Reflections at objects• Antenna polarization


Multi-Antenna Configurations

Crosstalk influenced by:• Antenna matching • Proximity effects • Reflections at objects• Antenna polarization• Circulator or directional coupler • Radiation pattern • Spatial configuration

Mono-static type Bi-static type

Crosstalk influenced by:• Spatial configuration• Radiation pattern • Reflections at objects• Antenna polarization


Measurement Example – Setup

• RX/TX antennas:off-the-shelfpatch antennasright hand circularly polarizedTX: 9 dBiRX: 7 dBipositions for best RX/TX decoupling: ~45 dB

• Tagoff-the-shelf EPCglobal UHF Class 1 Gen2

• Static scenario

• Distance to walls > 0.5m

BLF: 640 kHzPout: 32 dBmOutput: ADC samples


Antenna Setup

TXRX1

RX2

tag

tag2

antenna cables


Frontend Setup

16

rapid prototyping board

RX2

TX RX1PA

antenna cables to measurement room power meter

power dividerLO2

power dividerLO1

power supply


Signal to Interference

SIRRX1=-45.6 dBSIRRX2=-42.5 dB


SNR – Antenna Selection

SNRRX1=25.9 dBSNRRX2=30.2 dB

SNR improvement possible using antenna selection

Scatter plot with subtracted interference

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Summary

• Testbed conceptRapid prototyping board, analog frontends, antennas, 2×TX and 2×RX, flexibility due to modular approach

• UHF frontend concept

• Antenna configurationsMono-static, bi-static, and multi-antenna

• Measurement example1×transmitter and 2×receivers, SNR improvement possible due to antenna selection


Thank you!

[email protected]

www.nt.tuwien.ac.at/christian-doppler-laboratory/

www.nt.tuwien.ac.at/research/radio-frequency-engineering/

a testbed for multi-antenna applications in rfid

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